This study will attempt to analyze, define, and understand the mechanism of cellular control during the processes of regeneration, differentiation, and maturation of the hair and squamate epidermis. To provide a basis for experimental investigations further histological studies on the species variation of the squamate epidermis will be continued and enlarged. The shedding cycle of these animals will be evaluated in vivo with respect to season and hormonal alteration. Ultrastructural studies of the distinctive strata and their species variation will continue. Experimental studies on the biophysical relationships of the various strata will be evaluated. In vivo studies of protein and nucleic acid synthesis of the various strata of the squamate epidermis will be continued, compared with that of the lamprey, and the published work on mammalian epidermis and hair. Studies on the relationship between the shedding cycle and wound-healing in the squamates will be continued both at the histological, histochemical, and the ultrastructural level to further our understanding of the control mechanisms involved in cell movement, cell growth, differentiation and maturation. Organ culture of explants of squamte epidermis, and hair will be continued to evaluate specific factors, external, and intrinsic to the epidermis which control the cyclic alterations which occur within these organs. Variations in the structure of the cell membranes, cell organelles, and cytoplasm during maturation of the cells of the squamate epidermis will be studied by freeze-cleaving. Analysis of the pattern of DNA and protein-synthesis, in vivo and in vitro will be undertaken to form a basis for experimental alterations of these parameters.